A popular species on one of Scotland’s most important seabird islands has suffered a “catastrophic drop” of over 80% after a succession of winter storms, it can be revealed.
The European Shag population on the Isle of May in the Firth of Forth usually numbers in excess of 400 nesting pairs each summer, rising to 674 pairs of the red listed species last year.
The results of a population census carried out earlier this summer have now revealed the population has crashed to just 127 pairs, representing just 18.8% of last year’s total, amid fears the species may not recover at the site.
Concerns had been raised on the island, which is a National Nature Reserve (NNR) run by NatureScot – after the long-necked birds suffered heavy losses during Storm Babet and Storm Ciaran last October.
David Steel, NatureScot’s reserve manager on the island, said: “Over the last decade we’ve seen between 400-500 pairs nesting annually with 674 pairs nesting last year. However it’s a very different picture this year with the results of the population census in early June revealing a shocking 127 nesting pairs.
“This figure is the lowest in recorded history for the Isle of May dating back to the late 1950s and represents an 81% decline in just one year. This is a catastrophic drop and one which the species may not recover from.
“Unlike many seabirds, a lot of the population of Shags over-winter around the island and they are very susceptible to winter storms. Last October we had two major storms in quick succession – Storm Babet and Storm Ciaran– which brought heavy turbulent seas for weeks.
“During this period Shags were finding it difficult to find food and as a result mortality was extremely high.
“The species is extensively studied by UKCEH (UK Centre for Ecology & Hydrology) throughout the year as they map and charter each individual and their results were showing extremely worrying signs.
“The concern is now that the population has been decimated, what will the winter bring this year? Another poor spell and stormy conditions may drop the population further.”
The European Shag, Latin name Gulosus Aristotelis, is a long-necked bird around the size of a goose. Their name derives from the shaggy tuft on their heads.
The fish-eating bird nests across the Isle of May on the clifftops, gullies and rocky outcrops. They usually live for around 12 years although the record for the species is 31 years for a Shag ringed on the Shiant Isles in the Outer Hebrides.
The Isle of May Shag population peaked at 1916 pairs in 1987, before going into a decline seen across the UK over the next 30 years. Numbers in the last ten years have stabilised at 400-500 pairs nesting annually, rising to 674 last year before this year’s crash.
Mr Steel said the “wipeout” could be replicated at other sites on the east coast of Scotland, adding: “The majority of seabird colonies on the east coast with nesting Shags are reporting similar catastrophic drops. The future is worrying.”
Seabirds on the Isle of May have experienced mixed fortunes this year. The Atlantic Puffin population has enjoyed a 33% increase compared with the last count in 2017, with over 52,000 occupied burrows counted on the island this summer.
Arctic Terns made a welcome return, with over 300 nests counted just a year after the species failed to breed on the island in 2023. However, a Short-eared Owl not usually seen during the seabird breeding season devoured dozens of chicks.
